Short Technical Notes

 If WHERE clause does not have primary key in UPDATE query then this error comes. If you want to run the update query without having primary key in WHERE clause of UPDATE query then below command needs to be run to disable the safe mode. SET SQL_SAFE_UPDATES = 0; It is good to run  SET SQL_SAFE_UPDATES = 1;   after running your UPDATE query and again enable the safe mode. Example: SET SQL_SAFE_UPDATES=0; UPDATE table_name SET col_name=1; SET SQL_SAFE_UPDATES=1;

  If port 8080 needs to be kill use below single command: kill -9 $(lsof -t -i:8080) Note: remove -9 from the command, if you don't want to kill the process violently. To list any process listening to the port 8080: lsof -i:8080 Use any port number that you want to kill.

  A simple command will help to import and export collections in mongoDB. Export/Dump Collections in MongoDB: mongodump -d <database_name> -o <directory_backup> The above command will dump all the collections in the defined directory. eg: if your database name is awesome_db and you selected the my_db_backup as backup directory then you need run below command: mongodump -d awesome_db  -o my_db_backup If your db has authentication enabled then pass -u <username> -p <press enter> with the above command. Import/Restore Collection in MongoDB: mongorestore -d <database_name> <directory_backup> Similarly this command will restore the collections in the mongodb database.  for eg: mongodump -d awesome_db -o my_db_backup pass the authentication -u <username> -p <press enter> if your mongodb has authentiction. 

A virtual environment is the most used tool by the developers to isolate the dependencies for different projects. Suppose you have two projects say porj1 and proj2 . proj1 needs the Django dependency with version 3.2 but your proj2 needs the Django dependency with version 2.2. In this situation you need a virtual environment to keep the both version on your system separately.  How to create virtual environment in python:  Decide a directory where you want to create the virtual environment. You can use your project directory or any other directory as per your wish.  Run the below command. Here` awesome_proj_env ` is the folder where virtual environment will be created. if the folder does not exists then it will be created automatically. python3 -m venv awesome_proj_env    Activate the virtual environment: On Linux/Mac OSX: source awesome_proj_env/bin/activate  On Windows: awesome_proj_env \Scripts\activate.bat Deactivate the virtual environment in Python: type " deactivate "

Slice string in python: details= "Akshay Kumar Gupta--akshaygupta.me" # details[:6] and details[0:6] will give same result print(details[: 6 ]) # OUTPUT: Akshay # details[20:] and details[20:34] will give same result print(details[ 20 :]) # OUTPUT: akshaygupta.me # -1 denotes the reverse order print(details[ 11 ::- 1 ]) #OUTPUT: ramuK yahskA # Here -9 denotes the count from the end of the string print(details[:- 9 :- 1 ]) #OUTPUT: em.atpug #Both syntax gives the same result for reversing the string print(details[- 1 ::- 1 ]) #OUTPUT: em.atpugyahska--atpuG ramuK yahskA print(details[::- 1 ]) #OUTPUT: em.atpugyahska--atpuG ramuK yahskA Format print in python: print( "hi, My name is {} and I am a {}. I like {}." .format( "Akshay" , "Software Engineer" , "python" )) In the above print statement, "{}" refers to the placement of the values given in "format()" function. First value in the order "format()"

  1. Datatypes in Python: None Numeric float -> 1.5 int -> 5 complex -> 2+5j bool -> True/false Sequence List -> [3,5,6,7,1] Tuple -> (3,5,6,7,1) Set -> {3,5,6,7,1} String -> "Akshay" Range  range(5) -> range(0, 5)  list(range(5)) -> [0,1,2,3,4] list(range(2,10,2)) -> [2,4,6,8] Dictonary product_price = {'book': 50, 'pen': 300, 'eraser': 10}  product_price.get('book') -> 50 2. Number Conversion in Python bin( 28 ) -> 0b 11100 oct( 28 ) -> 0o 34  hex( 28 ) ->  0x 1c 3. Swap two numbers in Python           a = 5       b = 6 Method #1:             a, b = b, a Method #2            a = a + b         b = a - b         a = a - b 4. "math" module in python     import math math.sqrt(25) -> 5.0 math.floor(2.5) -> 2.0 math.ceil(2.5) -> 3.0 math.pow(2, 3) -> 8.0 math.pi -> 3.141592653589793 math.e -> 2.718281828459045 5. How to import a module in python import math import math as